A tap changer is known from DE 20 21 575 that has in total four vacuum switching tubes per phase. Provided in each of the two load branches are a respective vacuum switching tube as a main contact and a respective further vacuum switching tube, in series connection with a switch-over resistance, as resistance contact. In the case of uninterrupted load changeover from the previous winding tap n to a new, pre-selected winding tap n+1 initially the main contact of the side being switched off is opened and thereupon the resistance contact of the side taking over is closed so that an equalizing current limited by the switch-over resistances flows between the two taps n and n+1. After the previously closed resistance contact of the side switching off has opened, the main contact of the side taking over then closes so that the entire load current is conducted from the new winding tap n+1 to the load shunt; the changeover is concluded.
In DE 10 2009 048 813, which is not prior published, a further tap changer is described in which additionally further mechanical switches are provided between the electrical connection of the two vacuum switching tubes of each load branch and the load shunt.
The known tap changers require four separate vacuum switching tubes per phase. At the outset, the requirement for a large amount of space for these vacuum switching tubes is itself, as well as the associated actuating mechanism, disadvantageous. In addition such known constructions are relative expensive due to the high component outlay.